Conversion of hydrocarbon gases



J. A. GUYER V CONVERSION OF HYDROCARBON GASES Sept. 15, 1936.

Filed Aug. 2'7, 1934 uzmzwozoo moa EmzEmm INVENTOR.

ATTORNEYS.

n H -nun P30 WUW O PIU] JESSE A.'GUYER Patented Sept. 15, 1936 UNITED STATES PATENT OFFICE Jesse A. Guyer, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a. corporation of Delaware Application August 27, 1934, Serial No. 741,693

4 Claims.

This invention relates to the conversion of hydrocarbon gases into normally liquid hydrocarbons boiling in the motor fuel range.

There are produced in the cracking and distilling of 011; large quantities of hydrocarbon gas containing both parafiin and olefin hydrocarbons and suitable for conversion into gasoline. From natural gas there are extracted gaseous parafiin hydrocarbons, propane and butane, which likewise can be converted into gasoline. Various processes for the conversion of normally gaseous hydrocarbons into gasoline have been proposed. Gaseous oleilns under heat and pressure may be polymerized to gasoline. Gaseous paramn hydrocarbons, particularly propane and butane, may be converted into gasoline by heating under a high pressure to a cracking temperature ordinarily higher than that required for polymerizing oleflns, whereupon simpler olefins are formed by dissociation and normally liquid hydrocarbons then result from the polymerization reactions which ensue.

All the gaseous olefins, namely ethylene,

- propylene and the butylenes, cambe readily converted into polymers by heating under high pressure. Since the polymerizing tendency is nearly the same for them all, all these olefins will enter into reaction when a mixture is subjected to polymerizing conditions of heat and pressure, though paraflin hydrocarbons require temperatures so muchhigher than the olefins that a separate conversion step is desirable for olefin-rich and paraflin-rich gases respectively. A mixture of the gaseous parafilns, unlike the oleflns, cannot be converted. efliciently into gasoline hydrocarbons unless certain restrictions are placed on the composition of the mixture. The cracking velocity of the gaseous paraflins decreases rapidly with decrease in molecular weight. Methane 'is, of course, virtually inert and is accordingly undesirable. I have discovered that butane gives the highest yield of gasoline and is accordingly the most valuable of the gaseous paraifins, but

ethane and even propane, by reason of their more refractory character when accompanying butane are only'slightly cracked at the moderate temperatures required for cracking butane. Moreover,'these temperatures cannot be'exceeded if the formation of coke is to be avoided. Ethane and propane may be present in no more than a very small proportion if a reduced efficiency of the cracking step is to be avoided. I have found that very little ethylene is produced in the cracking of butane under high pressurebut that a substantial proportion of propylene is formed which may to advantage be separated from the reaction products and returned to the cracking operation. Small proportions of oleflns, preferably under 20%, may to advantage accompany butane, and in such a case will augment the 5 gasoline yield without necessitating any great reduction in the extent of conversion of the butane.

My invention provides a more economical means for producing gasoline from two gases, one predominantly paraflinic, and one containing a considerable quantity of oleflns. The invention provides for subjecting a mixture of gaseous hydrocarbons containing a substantial proportion of olefins to heat and pressure to effect polymerization of the oleflns into gasoline, then subjecting the surviving olefin-depleted gases to fractional distillation to efiect the removal from the mixture of specifically the methane and non-hydrocarbon gases, the ethane 20 and the small proportion of ethylene accompanying it, and at least a substantial part of the propane. The remaining gaseous hydrocarbons are mostly paraflinic and comprise butanes ior the most part, a small amount of butylenes and 25 preferably propylene and are subjected in a second conversion step to a cracking temperature at a high pressure to eiIect conversion into gasoline.

A hydrocarbon mixture oi this latter composi- 80 tion is peculiarly suitable for the reasons set forth for conversion under the rather drastic conditions of temperature and pressure required by parafflns, where a high conversion into gasoline is to he efiected in the heating operation. 35 The invention provides for effecting by a. single fractionating system the treatment of eiliuents from both high pressure conversion operations to produce a paraifinic charging stock meeting the strict requirements for efilcient conversion.

Gases suitable for treating in the olefin polymerization step in my process will contain 25% or more of olefins and may contain as high as of oleilns. Gases from cracking stills are suitable but gaseous concentrates obtained from 45 still gases by compression or absorption means and containing a lower proportion oi! methane are preferable. The olefin-rich gases may be subjected to press es of 500 to 1000 or 3000 pounds per square inch or more and temperatures 50 of 700 F. to 1000 F. to effect conversion and the paraffin-rich gases may be subjected to pressures of 1000 to 3000 pounds or more per square inch and 950 to 1100 F. to efiect conversion but in most cases a pressure or 3000 pounds per square inch and about 890 and 1020" F. respectively for the two operations give best results, the reaction time being on the order of two or three minutes in each case.

The advantages of my process will be apparent from the following description, taken in conjunction with the attached drawing, in which I is a pipe conveying olefin containing gases through the heat exchanger 2 and the furnace 3 to the exothermic reactor 4. In this furnace and reactor they will be maintained at pressures on the order of 2500 pounds per square inch, and at a temperature on the order of 890 F. From the reactor, the gases and polymers will pass back through the heat exchanger 2, which may be omitted if more heat is desired for the conduct of the subsequent fractionating steps, and through the transfer line 5 into the fractionating column 6 operated at suitable superatmospheric pressure but below 500 pounds per square inch. Paraffinic hydrocarbons of an average molecular weight of from 45 to '70, and which will usually predominate in butanes will be fed through the pipe I to the furnace 8 under pressures on the order of 2500 pounds per square inch, and cracked at temperatures on the order of 1020 F. From this furnace they may be passed through the scrubber 9, into which a cooling oil may be injected if desired, and through the heat exchanger i0, which may be omitted, into the line I! and the fractionator 6 substantially as shown. From the fractionator, gasoline and tar are removed as a kettle product, and the tar separated, if desired, in the fractionator l2. The overhead product, principally butane and lighter hydrocarbons, is withdrawn through the line 13 to the fractionator M, from which a kettle product consisting predominantly of butane is withdrawn through line i5 for recycling in the high temperature cracking coil. Light gases are discarded through the line I 9. A side stream predominating'in propane and propylene may be withdrawn from the fractionator l4, and injected into the side of the fractionator IS in which it is separated by highly efllcient fractionation into a propylene and lighter fraction, and a propane fraction, which is discarded. The propylene and lighter fraction may be recycled to either the polymerizing step or the cracking step as desired.

Oil not vaporized in the scrubber 9 may be passed around the fractionator 6 through the line I 8 to the fractionator l2 if desired.

The fractionating columns will, of course, be equipped with suitable refluxing and reboiling equipment, liquid level controls, and the like, here omitted for the sake of simplicity. Also, pressure reduction valves, pumps, and the like will be used wherever necessary. j

Many other slight modifications of my process will be apparent. For example, I may pass recycle stock from the line l5 through the heat exchanger l 0 and the line 20 to the furnace 8, introducing it into the reaction coil at an intermediate point if desired. I may also enclose both heating coils in the same furnace setting, regulating the supply of heat to each coil by means of dampers or equivalent means.

It is evident that my process will be operative on a wide variety of charging stocks. However, I prefer to charge to my high temperature cracking coil a material containing substantial quantitles of butanes, and to my polymerizing furnace any volatile hydrocarbon material containing substantial quantities of oleflns.

A wide range of operating pressures may be used in the fractionating columns shown as O and M in the accompanyingdrawing. In general, it will befound advantageous to operate the column 6 at pressures less than 500 pounds per square inch, and pressures on the order of 50 to 250 pounds per square inch will be found most suitable. 'When operating the column 8 .at the lower pressures, it will generally be found advantageous to insert a pump or compressor in the line l3, increasing the pressure in the column ll to 200 pounds per square inch or more. However, if refrigeration is available for cooling the reflux in the column l4, considerably lower pressures may be used. The column I! will normally be operated at pressures on the order of one or two atmospheres.

Having described my process, what I claim is:

1. The process of converting normally gaseous hydrocarbons to normally liquid hydrocarbons, which comprises subjecting olefin bearing gases to polymerization conditions of time and temperature at pressures in excess of 500 pounds per square inch while simultaneously subjecting predominantly parailinic hydrocarbons of an average molecular weight between 45 and 70 to pyrolysis conditions at pressures in excess of 1000 pounds per square inch, passing substantially all the products of the aforesaid polymerization and the major portion of the products of the aforesaid pyrolysis into a separating zone, separating them therein into a fraction consisting predominantly of gasoline and heavier hydrocarbons, and a fraction consisting predominantly of butane and lighter hydrocarbons, withdrawing the first mentioned fraction from the system while passing the aforesaid butane-containing fraction to a second separating zone, separating it therein into a fraction lighter than butane, and a fraction of high butane content, discarding the said lighter fraction, while passing the fraction of high butane content back for pyrolysis in admixture with the aforementioned predominantly paraflinic hydrocarbons.

2. The process for converting normally gaseous hydrocarbons into volatile normally liquid hydrocarbons which comprises heating an olefin-rich gas to a polymerizing temperature in a first heating zone, while maintaining it at a pressure in excess of 500 lbs. per square inch, heating a paraflln-rich gas consisting predominantly of butane to a' cracking and polymerizing temperature in a second heating zone while maintaining it at a pressure in excess of 1000 lbs. per square inch, passing substantially all the products from the first heating zone together with the products from the second heating zone into a first separating zone, there separating the products into a gasoline and heavier fraction, and a butane and lighter fraction, passing the butane and lighter fraction to a second separating zone, separating it therein into a light fraction and a fraction consisting predominantly of butanes, discarding the light fraction, and re-' turning the butanes to the second heatingsone.

3. The process for converting normally gaseous hydrocarbons into volatile normally liquid hydrocarbons which comprises heating an olefinrich gas to a polymerizing temperature in a first heating zone, while maintaining it at a pressure in excess of 500 lbs. per square inch, heating a iparaflin-rlch gas consisting predominantLv of butane to a cracking and polymerizing temperature in a second heating zone while maintaining it at a pressure in excess of 1000 lbs. per square ace-1,599

inch, passing substantially all the products from the first heating zone together with the products from the second heating zone into a first separating zone, there separating the products into a gasoline and heavier fraction, and a butane and lighter fraction, passing the butane and lighter fraction to a second separating zone, separating it therein into a light fraction, a fraction consisting predominantly of butanes, and a fraction rich in propylene and propane, passing the last mentioned fraction to a third separating zone, separating it therein into a fraction rich in propylene, and a fraction rich in propane, discarding the fraction rich in propane, and passing the fraction rich in propylene and the aforementioned fraction consisting predominantly of butanes back to the second heating zone for retreatment.

4. The process of converting normally gaseous hydrocarbons to normally liquid hydrocarbons, which comprises subjecting olefin bearing gases to polymerization conditions of time and temperature at pressures in excess of 500 pounds per square inch while simultaneously subjecte ing predominantly parafllnic hydrocarbons of an average molecular weight between and to pyrolysis conditions at pressures in excess of 1,000 pounds per square inch, passing substantially all the products of the aforesaid polymerization and the major portion of the products of the aforesaid pyrolysis into a separating system, separating therefrom a first fraction cons'isting predominantly of gasoline and heavier hydrocarbons and removing the fraction from the system, separating also a second fraction of high butane content and passing said second fraction back for pyrolysis, separating also a third fraction consisting of hydrocarbons lighter than the second fraction and discharging the last mentioned fraction from the system.

JESSE A. GUYER. 

